1. Field of the Invention
The disclosure discussed herein generally relates to a sheet amount indicator applicable to a sheet-feeding tray of an image forming apparatus, and an image forming apparatus having such a sheet amount indicator.
2. Description of the Related Art
In image forming apparatuses such as copiers, printers, and the like, sheets of paper are generally stored in a stacked fashion in a sheet-feeding tray serving as a paper container. The sheets of paper stored in the sheet-feeding tray are cut in predetermined dimensions and thus have a predetermined size. As illustrated in FIG. 12, such a sheet-feeding tray (101) may be disposed at a lower part of an image forming apparatus 100. The sheet-feeding tray 101 includes a base plate 102 movable in a vertical direction (i.e., an up-down direction), such that sheets of paper (hereinafter simply called “sheets”) 103 are set in a stacked fashion on the base plate 102. The base plate 102 is upwardly pressed by a spring 104 toward an upper side so as to allow a top sheet 103 to reach a not-illustrated pickup roller. The sheets are sequentially fed from the top sheet 103 into an image forming part of a main body of the image forming apparatus 100, thereby forming a desired image on each of the sheets. When the amount of sheets on the sheet-feeding tray is reduced and a small amount of sheets stacked on the sheet-feeding tray, a user may need to physically draw out the sheet-feeding tray from the main body of the image forming apparatus 100 in order to add or supply new sheets to the sheet-feeding tray in a stacked fashion.
The sheet-feeding tray generally includes a sheet amount indicator configured to indicate presence or absence of sheets, and an amount of sheets. It is possible for a user to check the amount of sheets by directly observing the sheets stacked on the tray while drawing out the sheet-feeding tray; however, in that case, the user may need to draw out the sheet-feeding tray every time the user desires to check the amount of sheets. Hence, printing tasks may be interrupted every time the user wishes to check the amount of sheets, which may degrade printing efficiencies. Moreover, when the image forming apparatus has suddenly stopped due to running out of sheets while performing a large amount of printing, it may be difficult to supply new sheets to the sheet-feeding tray promptly. Accordingly, the user generally supplies sheets to the sheet-feeding tray in advance while monitoring the sheet amount indicator from time to time in order to supply sheets to the sheet-feeding tray and restart the printing tasks promptly.
There are two types of the sheet amount indicator; a sensor type indicator and a mechanical type indicator. The sensor type sheet amount indicator is configured to detect an amount of sheets by a sensor and indicate the detected amount, whereas the mechanical type sheet amount indicator is configured to mechanically detect the amount of sheets and indicate the detected amount. Since the sensor type sheet amount indicator is expensive, the mechanical type sheet amount indicator is widely used. An example of the mechanical type sheet amount indicator is disclosed in Japanese Laid-open Patent Publication No. 2008-184246 (hereinafter referred to as “Patent Document 1”). In this example, the mechanical type sheet amount indicator 110 may be disposed on a lateral side of the sheet-feeding tray 101 as illustrated in FIG. 13.
The mechanical type sheet amount indicator 110 illustrated in FIG. 13 includes a first arm 112, one end of the first arm 112 being supported by a shaft 111 coaxial with a shaft 102a of a base plate 102, the other end of the first arm 112 being connected to a front end of the base plate 102; and a second arm 114 rotatable around a shaft 113 disposed on a lateral plate 101a of the sheet-feeding tray 101. One end of the second arm 114 includes an elongated slot 114a into which a pin 112a of the first arm 112 is inserted. The other end of the second arm 114 extends toward a front side of the sheet-feeding tray 101 in a paper-feeding direction. A projected indicator 114b formed on the other end of the second arm 114 is disposed inside a viewing part 120a formed in a front cover 120 of the sheet-feeding tray 101 as illustrated in FIG. 14.
When the sheets are loaded in full on the sheet-feeding tray 101, and the base plate 102 is forced to a lowermost position due to the weight of the loaded sheets as illustrated in FIG. 14, a tip of the first arm 112 is located at a lowermost position, and the indicator 114b of the second arm 114 is located at an uppermost position. When the loaded sheets run out, the tip 112b of the first arm 112 moves up to an uppermost position while the indicator 114b moves down to a lowermost position.
Further, a sheet amount indicator disclosed in Japanese Patent Application Laid-Open Publication No. 6-271141 (hereinafter referred to as “Patent Document 2”) includes a base plate, and a projection part formed on a front end of the base plate. The projection part formed on the front end of the base plate is configured to be engaged with a projection part of a rotatable display member arranged on a front cover of the sheet-feeding tray. In this configuration, the amount of sheets may be indicated when the display member is rotated according to movement of the base plate in a vertical (up-down) direction.